Have a look at
thegoodride.com. Independent reviews of men and women's snowboarding gear. It's a good starting point.
If she likes cruising at high speeds down east coast groomers. Check out boots with a high "response" rating and a full camber board. If she is usually going out in ideal conditions or more into casual cruising a hybrid camber/rocker board would be a better fit.
Besides riding style, weight and boot size are important in picking a board. Pretty much all manufactures have a chart for every board they make that shows what rider weights and boot sizes work for each board type. Also double check binding mounts. Industry standard is a 4x4 mount except for Burton which is pretty much pushing the channel mount on all of their gear now so if you buy non-burton EST bindings you will need an adapter to use a Burton board.
Hope this helps.